1. Field of the Invention
The present invention principally relates to a vibration detection apparatus for reducing noises generated as a result of vibration of cord, and a noise absorbent member for absorbing the noises.
2. Description of the Prior Art
A water-leakage detector 51 as shown in FIG. 6 has been heretofore used to detect a leakage of water in a water pipe laid under the ground. The water-leakage detector 51 comprises a vibration detecting apparatus 52 comprising a pickup 53 and a cord 54, a voltage amplifier 55 and a head-phone 56.
A water-leakage sound in the form of a fine vibration generated at a water-leakage point of the water pipe and propagated through the ground is picked up by the pickup 53 set on the ground to convert the sound into an electric signal, which is transmitted to the voltage amplifier 55 through the cord 54, and the electric signal is voltage-amplified to an audible level by the voltage amplifier 55. An operator listens to the amplified signal sound by the head-phone 56, and the presence or absence and position of the leakage of water are detected by the stress, pitch and the like.
In detecting the leakage of water, the operator holds the voltage amplifier 55 or places it on the stand to perform his work. Therefore, the cord 54 for connecting the pickup 53 to the voltage amplifier 55 is in an unstable state in the air. As a result, when the wind blows against the cord 54, the cord 54 finely vibrates in a horizontal direction to generate a wind-cut sound, and when the operator holds the cord 54 by his hand, the cord 54 finely vibrates in a vertical direction to generate a frictional sound.
On the other hand, since the water-leakage sound propagated through the ground is in the form of an extremely fine vibration, when the noise as described above is picked up by the pickup 53, the noise cannot be sufficiently discriminated from the water-leakage sound to impede the detection of leakage of water. Thus, the utmost care should be paid so as not to generate the noise as described above, deteriorating the efficiency of the water-leakage detection work.
In view of the foregoing, a vibration detecting apparatus 62 as shown in FIG. 7 has been invented and used to damp the noise as described above before it is picked up by the pickup 53. In this vibration detecting apparatus 62, a cord 64 is formed with a winding portion 64a, in addition to the constitution of the vibration detecting apparatus 52 shown in FIG. 6. Since the vibration direction is changed by the winding portion 64a, the noise can be damped, and since the winding portion 64a comprises an inertia mass, the noise can be absorbed.
However, in the vibration detecting apparatus 62 shown in FIG. 7, the winding portion 64a is oscillated by the wind or expanded and contracted in a vertical direction whereby the adjacent cord portions of the winding portion 64a collide with each other to generate a large frictional sound.